Systems for closed loop control of the behavior of motor vehicles are known from the related art with many different modifications. For example, anti-lock control systems, as well as traction control systems are known which aim to largely maintain the usual vehicle behavior even in situations that are critical with respect to longitudinal dynamics. Moreover, control systems are also known, such as all-wheel drive under open- or closed-loop control, chassis control or driving dynamics control. The aim of these systems is to influence the vehicle such that it maintains its usual driving behavior even in situations that are critical with respect to transverse dynamics.
All of the systems named above have in common that nominal quantities are generally determined from measured and estimated quantities. By comparing these nominal quantities with actual values determined, for example, using sensors, regulated quantities are determined. Using these regulated quantities, actuators located in the vehicle are activated. Through the intervention performed by the actuators, the behavior of the vehicle is influenced such that the actual value approaches the specified nominal quantity.
For the above named systems, the importance of transverse acceleration as a measured quantity varies in importance. In some of the above named systems, an existing transverse acceleration is taken into account such that for an existing transverse acceleration, the regulated quantities that are determined to actuate the actuators are corrected as a function of its value.
Thus, for example, DE-OS 34 21 732 discloses an anti-lock control system with which the driving behavior of a vehicle is improved during a braking operation in travel through a curve. For this purpose, this anti-lock control system is equipped additionally with a transverse acceleration sensor whose measured value is compared during the braking operation with a threshold value. Where the measured values exceeds the threshold value sensor, the intake valve for the rear axle is driven such that, for at least a time period, the braking pressure in the wheel brake cylinders of the rear axle is increased only slightly or rather not at all. In this case, the rear axle maintains nearly the full lateral stability, the driving behavior of the vehicle being improved as a result during the braking operation in travel through a curve.
Likewise, DE-OS 34 21 700 discloses an anti-lock control system that is equipped with a transverse acceleration sensor. As is generally known, considerable yawing moments can occur on roadways with highly asymmetrical coefficients of friction due to a braking performed by an anti-lock control system, since the wheels on the dry-roadway vehicle side grip and retard the vehicle, but the wheels on the slippery-roadway vehicle side do not. In order to avoid the high yawing moments in this case, the braking pressure on the wheel with a higher coefficient of friction is limited as a function of the braking pressure on the wheel with a lower coefficient of friction. Admittedly, the same variable braking forces occur also when braking in curves, where a high transverse acceleration is simultaneously present. In this case, however, a limitation of the yawing moment that does not permit the optimum braking forces at the start of the braking is harmful. In order to be able to differentiate the two above named situations (braking in a curve and braking on a roadway with highly asymmetrical coefficients of friction), a conventional anti-lock control system is equipped with a transverse acceleration sensor. The measured value of the transverse acceleration sensor is compared with a specified transverse acceleration threshold. If the transverse acceleration threshold is exceeded, i.e., if travel through a curve is detected, a further pressure build-up is permitted on the wheel having the higher coefficient of friction. Thus, the yawing moment limitation is changed or rather, under certain circumstances, partially canceled. Accordingly, with the installed transverse acceleration sensor, one achieves, on the one hand, the desired driving stability when braking in a curve and, on the other hand, the desired improvement in the manageability on asymmetrical roadways.
In addition to the anti-lock control systems, the transverse acceleration can also be significant in traction control systems. German Patent 34 17 423 describes a propulsion control device for a vehicle in which the reduction of the engine torque is carried out as a function of a measured transverse acceleration. Here, it is decided as a function of a comparison of the measured value of the transverse acceleration with a specified value for the transverse acceleration whether the reduction of the engine torque, is carried out as soon as a driven vehicle wheel exhibits a wheelspin tendency or, when both driven vehicle wheels exhibit a wheelspin tendency.
As mentioned above, the transverse acceleration is taken into account inter alia also in chassis control. Thus, German Published Unexamined Application DE-OS 41 21 954 describes a process for obtaining yaw rate and/or transverse speed, to be used, for example, in chassis control. For this purpose, the transverse acceleration and the steering angles of the two axles are measured using sensors. Based on these measured quantities, the yaw rate and the vehicle transverse speed are estimated using a state estimator. These quantities can then be further processed in the context of chassis control.
The transverse acceleration is also significant in driving dynamics control systems. Such a system is disclosed, for example, by German Published Unexamined Application DE-OS 42 43 717. It describes a process for closed loop control of a vehicles stability. In this process, a yaw rate setpoint value is determined and a yaw rate actual value is measured. By comparing the two quantities, the deviation of the actual value from the setpoint value is obtained. As a function of this deviation, braking pressure control valves are driven such that an additional yawing moment is produced to adjust the actual value to the setpoint value. This application reveals two possible ways for computing the yaw rate setpoint value. This application, it shows how to compute the yaw rate setpoint value based on the steering angle and vehicle speed. This type of computation applies for the linear range. This application also shows that the yaw rate setpoint value can be computed as a function of the transverse acceleration and the vehicle speed. This type of computation applies for the nonlinear range.
In the publication "FDR-Die Fahrdynamikregelung von Bosch" [FDR-Driving dynamics control from Bosch] which appeared in "Automobiltechnische Zeitschrift" (ATZ) 96 (1994) [Automobile Engineering Journal] on pp. 674-689, a driving dynamics control system is likewise described. One skilled in the art understands from this article, e.g., in FIG. 5 on page 677, among other things, the use of a transverse acceleration sensor to measure the transverse acceleration from which estimated quantities are determined (see FIG. 4 on the same page in this context).
Based on the examples given above, it is understood that the transverse acceleration has great significance as a measured quantity in relation to closed-loop control of vehicle behavior. Under certain circumstances, a measured transverse acceleration riddled with errors can result in faulty behavior of the closed-loop control.
In the normal case, the transverse acceleration is measured using a transverse acceleration sensor. This measurement of the transverse acceleration takes place in an inertial system. Besides the transverse forces that act upon the vehicle due to the vehicle motion, the forces caused by a transversely inclined roadway also enter into the value of the measured transverse acceleration. However, the control processes described above for computing necessary quantities are based customarily on roadway-fixed coordinate systems. Such roadway-fixed coordinate systems have the property that the roadways in the systems exhibit no transverse inclination, and the transverse acceleration used therein consequently does not reflect any components brought about by a transverse inclination of the roadway. Due to this situation (measured transverse acceleration in an inertial system and required transverse acceleration in a roadway-fixed coordinate system), one would make an error if one were to use the transverse acceleration measured in the inertial system directly without compensating for this aspect of the roadway-fixed coordinate system.
In German Patent 43 25 413, a process for determining quantities characterizing the driving behavior is described in which this problem (usage of a transverse acceleration measured in an inertial system in a roadway-fixed coordinate system) is taken into account. The starting point of this process are motion equations which describe the transverse or rather longitudinal dynamics of the vehicle in the plane. These motion equations are supplemented with measurement equations based on a vehicle model. In this approach, the transverse inclination of the roadway is taken into account as a state quantity. Thus, the quantities characterizing the driving behavior can be determined which take into account the transverse inclination of the roadway. Measured quantities entering into this process are the vehicle longitudinal speed, the longitudinal acceleration of the vehicle, the transverse acceleration of the vehicle, the yaw angle speed of the vehicle, the steering angle and the wheel speeds of the individual wheels. The process is used among other things for computing the float angle.
The object of the present invention is to optimize existing systems for controlling in closed loop quantities representing vehicle motion such that in measuring the transverse acceleration, the transverse inclination of the roadway is taken into account. The determined transverse inclination of the roadway can thus be drawn upon for correcting the transverse acceleration measured in an inertial system and used in a roadway-fixed coordinate system.